“We are concerned about Attorney General Sessions' lack of candor to the committee and his failure thus far to accept responsibility for testimony that could be construed as perjury,” the senators wrote in an initial letter dated in March.

They would send another letter dated April 28, and yet another dated May 12 — just days after President Trump abruptly fired Comey.

U.S. Attorney General Jeff Sessions.

(Yuri Gripas/REUTERS)

The letters did not detail what the suspected third meeting might have been. But NBC News reported Thursday that the FBI and Congress are looking into a small gathering of Trump, Sessions, Kislyak and Trump's son-in-law Jared Kushner at the Mayflower Hotel in Washington, D.C. last spring.

Leahy and Franken both asked Sessions during his nomination hearing if he was in touch with any Russian officials during Trump’s campaign, and the Alabama senator denied any contact.

But the Washington Post reported in March that Sessions had spoken twice with Russian Ambassador Sergey Kislyak during the campaign.

CNN reported Wednesday that congressional investigators were working to determine if Sessions and Kislyak had a third meeting that had also not been disclosed.

In a joint statement on Thursday, Leahy and Franken said they worried Sessions “still not been forthcoming about the extent of his contacts with Russian officials.”

“We know he would not tolerate dishonesty if he were in our shoes. If it is determined that the attorney general still has not been truthful with Congress and the American people about his contacts with Russian officials during the campaign, he needs to resign,” the statement said.